JP2018020421A - Power tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect a kick-back of rebounding a power tool from a workpiece, from a behavior of a power tool body.SOLUTION: A power tool comprises a motor, a driving circuit for driving the motor, a control part for controlling driving of the motor via the driving circuit, a device body for storing these respective parts and capable of installing a tip tool rotatingly driven by the motor and a detection part for detecting an attitudinal change in the device body. The control part stops the driving of the motor by determining that the device body is rebounded from a workpiece when an attitudinal change amount of the device body detected by the detection part exceeds a preset threshold value.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to an electric power tool used for processing a workpiece by rotating a tip tool.

  For example, in a power tool that processes a workpiece by rotating a disk-shaped tip tool, such as a grinder, when the tip tool is rotated and brought into contact with the workpiece, the workpiece is reacted with the tip tool. A force may be applied, causing the tool body to bounce off the workpiece.

  When such rebounding (hereinafter also referred to as kickback) occurs, the load applied to the motor from the tip tool is rapidly reduced, so that the rotational speed of the motor is rapidly increased. Therefore, conventionally, when the rate of change in the rotation speed of the motor exceeds the threshold value, it is determined that the electric tool has rebounded from the workpiece (in other words, kickback has occurred), and the driving of the motor is stopped. It has been proposed (see, for example, Patent Document 1).

Japanese Patent Publication No. 64-6898

  However, the load applied to the motor is not limited to when the electric tool is bounced off the workpiece, for example, when the workpiece is cut and the tip tool is released from the workpiece, or when the user uses the electric tool. Even when the is separated from the work piece, it rapidly decreases.

  For this reason, if the kickback is detected from the rate of change in the rotation speed of the motor as described above, the probability of false detection of the kickback is increased, and the motor is driven even though no kickback has occurred. May be stopped, giving the user a sense of incongruity.

  An object of one aspect of the present disclosure is to enable accurate detection of kickback in which an electric power tool bounces off a workpiece from the behavior of the electric power tool body.

  An electric tool according to one aspect of the present disclosure includes a motor, a drive circuit that drives the motor, a control unit that controls driving of the motor via the drive circuit, and an apparatus main body. The apparatus main body houses a motor, a drive circuit, and a control unit, and is configured so that a tip tool that is rotationally driven by the motor can be attached.

  In addition, the power tool is provided with a detection unit for detecting the posture change of the apparatus main body, and the control unit presets the amount of change in the posture of the apparatus main body detected by the detection unit when the motor is driven. When the set threshold value is exceeded, it is determined that the apparatus main body is rebounded from the workpiece.

  That is, the control unit detects that the apparatus main body has bounced back from the workpiece (kickback) not from the number of rotations of the motor but from a change in the attitude of the apparatus main body. And a control part will stop the drive of a motor, if a kickback is detected.

  For this reason, according to the electric tool of the present disclosure, it is possible to improve the accuracy of detecting the kickback as compared with the conventional device that detects the kickback from the rate of change in the rotation speed of the motor. Therefore, it is possible to prevent the user from feeling uncomfortable by erroneously detecting kickback and stopping the driving of the motor.

Here, the detection unit may be configured to detect at least one of the movement speed and the movement amount of the apparatus main body in one or a plurality of axial directions as the posture change amount of the apparatus main body.
In this case, the control unit determines that the apparatus body is rebounded from the workpiece (in other words, kickback has occurred) when the movement speed or movement amount detected by the detection unit exceeds the threshold value, You may be comprised so that the drive of a motor may be stopped.

  In this way, the control unit can detect the kickback and stop the driving of the motor when the apparatus main body moves in a predetermined axial direction at high speed or in a short time. .

The detection unit may be configured to detect at least one of the rotation speed and the rotation amount around one or more axes of the apparatus main body as the posture change amount of the apparatus main body.
In this case, the control unit determines that the apparatus body is rebounded from the workpiece (in other words, kickback has occurred) when the rotation speed or rotation amount detected by the detection unit exceeds the threshold value, You may be comprised so that the drive of a motor may be stopped.

  In this way, the control unit determines that kickback has occurred when the apparatus main body rotates around the predetermined axis at high speed or in a short time, and stops driving the motor. be able to.

  Next, when the motor is driven, the control unit determines that the electric tool is in the process of processing the workpiece when the load applied from the tip tool to the apparatus main body is larger than the threshold for determination during the operation. You may provide the determination part.

  In this case, when the determination unit determines that the workpiece is being processed, the control unit determines whether the apparatus main body has bounced off the workpiece based on the posture change amount of the apparatus main body (in other words, In this case, it may be configured to determine whether or not a kickback has occurred.

  In this way, the period during which the control unit determines the occurrence of kickback can be limited when the electric tool is processing the workpiece and there is a possibility that kickback will occur. Therefore, in this case, it is possible to suppress the kickback from being erroneously detected under a condition in which the kickback does not occur, and to improve the kickback detection accuracy.

By the way, when a kickback occurs during the processing operation of the workpiece, the load applied from the tip tool to the motor and thus to the apparatus main body is reduced.
For this reason, if the determination period of the kickback is simply set when the load applied to the apparatus main body from the tip tool is larger than the threshold value, the determination period before the kickback is detected when the load sharply decreases due to kickback. It is conceivable that kickback cannot be detected after the elapse of time.

  Therefore, the determination unit determines that the electric tool is to be processed during a period from when the load exceeds the threshold value for determining the start of work until the load falls below the threshold value for determining the end of work and until a certain delay time elapses thereafter. You may be comprised so that it may determine with it being in the process operation of material.

  In this way, the kickback determination period set by the determination operation of the determination unit can be set to include a period during which the load decreases with the occurrence of kickback, and the kickback detection accuracy can be set. Can be further enhanced.

  Note that the load for setting the kickback determination period as described above can be detected from the rotational torque of the motor from the tip tool, the current flowing to the motor, the rotational speed of the motor, etc. It can also be detected from vibrations that occur.

It is an external view showing the structure of the grinder of embodiment. It is a block diagram showing the structure of the whole drive system of a grinder. It is a flowchart showing the motor drive control process performed with a control circuit. It is a time chart explaining a kickback determination period.

Embodiments of the present invention will be described below with reference to the drawings.
In the present embodiment, a grinder will be described as an example of the electric tool of the present disclosure.
As shown in FIG. 1, the main body portion (apparatus main body) of the grinder 2 of this embodiment is mainly composed of a motor housing 4, a gear housing 6, and a rear cover 8.

  The motor housing 4 is a substantially cylindrical housing and houses the motor 20. The motor 20 is housed in the motor housing 4 such that the rotation shaft is parallel to the central axis of the motor housing 4, and one end of the rotation shaft protrudes toward the gear housing 6.

The rotating shaft of the motor 20 is connected to a spindle 12 that protrudes outside from the gear housing 6 via a gear mechanism provided in the gear housing 6.
The spindle 12 is rotatably provided in the gear housing 6 so that the center axis is orthogonal to the rotation axis of the motor 20, and the gear mechanism in the gear housing 6 converts the rotation of the motor 20 into the rotation of the spindle 12. Thus, it is configured using a bevel gear or the like. Since the gear mechanism has the same configuration as a general grinder, detailed description thereof is omitted here.

  Next, the spindle 12 protruding from the gear housing 6 is provided with an inner flange 14 for positioning and fixing the disc-shaped tip tool 16. A lock nut 18 for clamping the tip tool 16 between the inner flange 14 and the inner flange 14 is screwed into the tip end side of the inner flange 14 of the spindle 12.

  For this reason, by providing the tip tool 16 between the inner flange 14 and the lock nut 18 and tightening the lock nut 18 to the inner flange 14 side, the tip tool 16 can be firmly fixed.

  In the grinder 2 of the present embodiment, a grinding wheel, a cutting wheel, a wire brush, or the like can be used as the tip tool 16, and the tip tool 16 can be detachably attached to the grinder 2.

  Further, in the gear housing 6, a wheel cover 19 is fixed around the protruding portion of the spindle 12 to protect the user from scattering of workpieces and tip tools 16 generated during operations such as grinding, polishing, and cutting. Has been.

Further, a grip mounting hole 7 is provided on the side wall of the gear housing 6 so that a user can attach a grip for gripping by hand.
Next, the rear cover 8 is provided on the opposite side of the motor housing 4 from the gear housing 6. From the rear end on the opposite side of the gear housing 6, a commercial power source that is an AC power source 10 (see FIG. 2) is provided. A power cord 9 for receiving power supply is drawn out.

  The power cord 9 has a power plug that can be connected to the outlet of the AC power source 10 at the tip, and the AC power can be supplied from the AC power source 10 to the grinder 2 by inserting the power plug into the outlet. Yes.

  In the rear cover 8, a controller 50 for driving and controlling the motor 20 with AC power supplied from the AC power supply 10 is housed. On the side wall of the motor housing 4, there is provided an operation switch 30 for conducting and interrupting an energization path for supplying power from the power cord 9 to the controller 50 (and thus the motor 20).

  The controller 50 is configured by mounting various circuit components shown in FIG. 2 on a circuit board. In FIG. 1, this circuit board is described as the controller 50.

  Next, as shown in FIG. 2, the operation switch 30 is provided in each of two energization paths that connect the AC power supply 10 and the controller 50 (and thus the motor 20), and is a pair that conducts and blocks the energization paths. Contact points 32 and 34.

  The user can turn on and off the contacts 32 and 34 substantially simultaneously by sliding the operation portion of the operation switch 30 exposed outside the motor housing 4.

  The motor 20 is a commutator motor (so-called brush motor) having a mechanical commutator and a brush for switching the current flowing through the armature according to the rotation phase and maintaining the rotation moment in a certain direction.

  In the present embodiment, a single-phase series-winding commutator motor (so-called universal motor) in which the armature 22 and the field windings 24 and 26 are connected in series and can be driven by either AC or DC is used.

  The controller 50 is provided with an energization path for connecting both ends of the motor 20 to the respective contacts 32 and 34 of the operation switch 30. The energization path for connecting the contact 32 and the motor 20 includes a bidirectional thyristor 52. And a resistor 57 is provided.

  The resistor 57 is for detecting a current (motor current) flowing through the motor 20, and the resistor 57 is connected to a current detection circuit 58 that detects the motor current from the voltage across the resistor 57.

  The bidirectional thyristor 52 is a current-driven semiconductor element. In this embodiment, when the operation switch 30 is in the on state, the on / off state is switched according to a command from the control circuit 80, and It is used as a switching element that controls the energization current.

  The controller 50 detects a drive circuit 60 for driving the bidirectional thyristor 52, a switch detection circuit 54 for detecting the operation state of the operation switch 30, and a zero cross point of the AC voltage supplied from the AC power supply 10. A zero-cross detection circuit 56 is provided.

  The switch detection circuit 54 is configured to detect that the operation switch 30 has been turned on from a voltage change in the energization path between the contact 34 of the operation switch 30 and the motor 20.

  The zero-cross detection circuit 56 is connected to the energization path on the AC power supply 10 side of the contact 34 of the operation switch 30 and is configured to detect the zero-cross point of the AC voltage from the voltage change of the path.

  The switch detection circuit 54, zero cross detection circuit 56, current detection circuit 58, and drive circuit 60 are connected to the control circuit 80. The control circuit 80 is also connected to a speed setting unit 42 operated by the user and a display unit 44 that displays the state of the grinder 2.

The control circuit 80 corresponds to the control unit of the present disclosure, and is configured by an MCU (Micro Controller Unit) including a CPU, a ROM, a RAM, and the like.
Then, the control circuit 80 moves the bidirectional thyristor 52 from the zero cross point detected by the zero cross detection circuit 56 according to the driving speed set via the speed setting unit 42 when the operation switch 30 is in the ON state. The motor current is controlled by adjusting the time until turning on. Further, the control circuit 80 displays the operation state of the grinder 2 on the display unit 44.

  The drive circuit 60 is configured to flow current to the gate of the bidirectional thyristor 52 in accordance with a control signal output from the control circuit 80, turn on the bidirectional thyristor 52, and flow current to the motor 20. ing. For this reason, the control circuit 80 can control the current flowing through the motor 20 via the drive circuit 60.

  In addition, the controller 50 is provided with a power supply circuit 70 for generating a power supply voltage (DC voltage) Vcc for driving internal circuits including the control circuit 80. The power supply circuit 70 operates by receiving power directly from the AC power supply 10 so that the control circuit 80 can operate even when the operation switch 30 is in the OFF state.

  That is, the power supply circuit 70 includes a Zener diode 71, a capacitor 72, and a resistor 73 connected to the energization path on one end side of the AC power supply 10 to which the contact 32 of the operation switch 30 is connected. The other end of each part is connected via a resistor 74 and a diode 76 to an energization path on the other end side of the AC power supply 10 to which the contact 34 of the operation switch 30 is connected.

  The Zener diode 71 generates the power supply voltage Vcc with its own breakdown voltage. The cathode is connected to the power supply line in the controller 50 and connected to the energization path between the AC power supply 10 and the contact 32. Has been. The anode of the Zener diode 71 is connected to the ground line of the controller 50.

  The capacitor 72 is connected in parallel to the Zener diode 71 to stabilize the power supply voltage Vcc. The resistor 73 is for removing charges accumulated in the capacitor 72 after the power cord 9 is disconnected from the AC power source 10.

  The diode 76 has an anode connected to the anode side (that is, a ground line) of the Zener diode 71 via a resistor 74, and a cathode connected to an energization path between the AC power supply 10 and the contact 34.

  For this reason, the diode 76 functions as a rectifier circuit that limits the current flowing from the AC power supply 10 to the power supply circuit 70 in one direction. The resistor 74 is for absorbing a voltage change obtained by subtracting the breakdown voltage of the Zener diode 71 and the forward voltage of the diode 76 from the output voltage of the AC power supply 10.

  The motor 20 is a commutator motor, and the mechanical commutator with which the brush contacts changes according to the rotation of the motor 20, so that high frequency noise higher than the frequency of the AC power supply 10 is generated. For this reason, a capacitor 40 for absorbing the noise is provided between the two energization paths from the AC power supply 10 to the controller 50.

  The grinder 2 of the present embodiment configured as described above allows the motor to be controlled under the control of the control circuit 80 if the user operates the operation switch 30 while holding the motor housing 4 or the like that is the apparatus body. 20 is driven and the tip tool 16 rotates.

  In this state, if the tip tool 16 is brought into contact with the machining position of the workpiece, the workpiece can be machined by the tip tool 16, but when the tip tool 16 is brought into contact, the workpiece is transferred from the workpiece to the apparatus main body. Since a reaction force is applied, the apparatus body may be rebounded by the reaction force.

  When the main body of the apparatus is bounced (in other words, when kickback occurs), the tip circuit 16 may hit the member around the workpiece and be damaged, so that the control circuit 80 generates the kickback when the motor 20 is driven. Is automatically detected and the motor 20 is stopped.

  In the present embodiment, the controller 50 is provided with an acceleration sensor 82 and an angular velocity sensor 84 so that kickback can be detected from a change in the posture of the apparatus main body, and detection signals from these sensors 82 and 84 are also detected. Input to the control circuit 80.

  The acceleration sensor 82 is configured by a three-axis acceleration sensor that can detect accelerations in directions of three axes (X axis, Y axis, Z axis) orthogonal to each other in the apparatus main body. The angular velocity sensor 84 is configured by a three-axis angular velocity sensor that can detect angular velocities (for example, pitch, roll, yaw) around three axes (X axis, Y axis, Z axis).

  The sensors 82 and 84 are assembled to the controller 50 such that the rotation center axis of the motor 20 is the X axis, the rotation center axis of the spindle 12 is the Y axis, and the direction perpendicular to these axes is the Z axis. It has been.

  However, the acceleration sensor 82 and the angular velocity sensor 84 need only be able to detect a change in the attitude of the apparatus main body at the time of kickback, so it is not necessary to be integrated with the controller 50, and the motor housing 4 and gear housing 6 constituting the apparatus main body. It may be assembled to. Further, the acceleration sensor 82 and the angular velocity sensor 84 are not necessarily a triaxial sensor, and may be a biaxial or uniaxial sensor.

Next, a motor drive control process executed by the control circuit 80 to drive the motor 20 will be described with reference to the flowchart shown in FIG.
The motor drive control process is a process repeatedly executed as one of the main routines in the control circuit 80. First, in S110 (S represents a step), it is determined whether or not the operation switch 30 is in an ON state. .

  If the operation switch 30 is in the ON state, it is determined whether or not the grinder 2 is in an error state by determining whether or not an error flag that is set when a kickback occurs is set in a process that will be described later. to decide.

  If it is determined in S120 that the error flag is set and the grinder 2 is in an error state, the process proceeds to S110. If it is determined that the grinder 2 is not in an error state, the process proceeds to S130.

  In S130, the gravitational acceleration component is removed from the acceleration detection signal by filtering the triaxial acceleration detection signal input from the acceleration sensor 82, and the process proceeds to S140. Note that the filtering process of S130 is executed as a high-pass filter having a cutoff frequency of about 1 to 10 Hz, for example.

  Next, in S140, it is determined whether or not the motor current detected by the current detection circuit 58 exceeds a preset "threshold 1". If the motor current exceeds "threshold 1", S150 is determined. Then, it is determined whether or not the state has exceeded the set time “t1”.

  If it is determined in S150 that the motor current exceeds “threshold 1” for a set time “t1” or longer, the load applied to the motor 20 from the tip tool 16 is large, and the workpiece It is determined that the machining operation is being performed, and the process proceeds to S160. In S160, the working flag is set, and the process proceeds to S210.

  On the other hand, if it is determined in S150 that the motor current has exceeded “threshold 1” and the set time “t1” has not elapsed, the process proceeds to S170, and the in-operation flag is currently set. In step S210.

On the other hand, if it is determined in S140 that the motor current does not exceed “threshold value 1”, the process proceeds to S180 to determine whether or not the motor current is less than “threshold value 2”.
As shown in FIG. 4, a current value smaller than “threshold value 1” is set in “threshold value 2”, and in S180, the load applied to motor 20 from tip tool 16 from the motor current is the workpiece. It is judged whether it is lower than during the machining operation.

  When it is determined in S180 that the motor current is less than “threshold value 2”, the process proceeds to S190, where it is determined whether or not the state has exceeded the set time “t2”. If t2 or more has elapsed, the process proceeds to S200. In S200, the working flag is cleared, and the process proceeds to S210.

  If it is determined in S180 that the motor current is equal to or greater than “threshold 2”, or if it is determined in S190 that the set time “t2” or more has not elapsed, the process proceeds to S170. Thus, the working flag is kept in the currently set state, and the process proceeds to S210.

  Here, the “threshold value 1” is that the load applied to the motor 20 from the tip tool 16 is increased after the tip tool 16 is brought into contact with the workpiece for machining the workpiece after the motor 20 starts driving. Is based on the motor current and is a threshold value for work start determination according to the present disclosure.

  The “threshold value 2” indicates that the load applied to the motor 20 from the tip tool 16 has decreased since the tip tool 16 has been separated from the workpiece since the processing of the workpiece by the grinder 2 has started. This is a threshold for determining the completion of work according to the present disclosure.

  In S140 to S200, as shown in FIG. 4, when the motor current becomes larger than “threshold 1” and the state has exceeded the set time “t1”, the in-work flag is set, and the current workpiece is processed. It is memorized that the machining operation is being performed.

  Once the working flag is set, the motor current falls below “threshold 2”, and then the working flag is set until a certain delay time (that is, set time “t2”) elapses. When the set time “t2” elapses, the working flag is cleared. In the present embodiment, the processes of S140 to S200 correspond to the determination unit of the present disclosure.

  The in-work flag is for defining a kickback determination period. In S210, it is determined whether the in-work flag is currently set by determining whether the in-work flag is set. To do.

  If it is determined in S210 that the in-operation flag is not set, it is not the current kickback determination period, so the process proceeds to S220 to S240, and various integration values used for kickback determination in the processing described later are reset. To do.

  Specifically, in S220, the moving speed that is an integral value of the acceleration detection value calculated in S260 described later is set to an initial value (0), and in S230, the moving speed calculated in S270 described later is set. The movement amount that is an integral value is set to an initial value (0). In S240, the rotation angle, which is an integral value of the angular velocity detection value calculated in S280 described later, is set to an initial value (0).

Then, after executing the processing of S220 to S240, the process proceeds to S250, the motor 20 is driven, and the process proceeds to S110.
Next, if it is determined in S210 that the in-work flag is set, whether or not the grinder 2 has bounced off the workpiece from the attitude change of the grinder 2 (in other words, a kickback has occurred) To determine whether or not).

  In S260, the detected values of the accelerations in the three-axis directions detected by the acceleration sensor 82 are integrated to detect the moving speeds of the main body of each apparatus, and in S270, the moving speeds are respectively integrated. As a result, the amount of movement of the apparatus main body in each axial direction is detected.

  In subsequent S280, by detecting the angular velocity detection values around the three axes detected by the angular velocity sensor 84, the rotation amount (in other words, the rotation angle) around each axis of the apparatus main body is detected. Migrate to

  In S290, at least one of the movement speeds or movement amounts in the respective axial directions detected in S260 and S270 is a kickback determination value set in advance for determining kickback (specifically, determination speed or determination movement amount). It is judged whether it is larger than.

  If it is determined in S290 that at least one of the movement speed or movement amount in each axial direction is larger than the kickback determination value, the posture change of the apparatus main body is large, and the kickback in which the grinder 2 is rebounded from the workpiece is performed. It is determined that it has occurred, and the process proceeds to S310.

  On the other hand, if it is determined in S290 that the moving speed and moving amount in each axial direction are all equal to or less than the kickback determination value, it is determined that the kickback cannot be detected with the moving speed or moving amount in each axial direction. Then, the process proceeds to S300.

  In S300, at least one of the acceleration around each axis detected by the angular velocity sensor 84 or the rotation angle around each axis detected in S280 is a preset kickback determination value (specifically, a determination angular velocity). Alternatively, it is determined whether or not the angle is larger than the determination angle.

  If it is determined in S300 that at least one of the angular velocity or rotation angle around each axis is larger than the kickback determination value, the posture change of the apparatus main body is large, and a kickback is generated in which the grinder 2 is rebounded from the workpiece. The process proceeds to S310.

In S310, since it is determined that kickback has occurred, an error flag is set, and in S320, the driving of the motor 20 is stopped, and then the process proceeds to S110.
In S300, if it is determined that the angular velocity and the rotation angle around each axis are all equal to or less than the kickback determination value, the kickback could not be detected even at the angular velocity or rotation angle around each axis (in other words, It is determined that no kickback has occurred), and the process proceeds to S250. In S250, the motor is driven as described above, and the process proceeds to S110.

  Next, if it is determined in S110 that the operation switch 30 is not in the on state (that is, it is in the off state), it is not necessary to drive the motor 20, so the process proceeds to S330 and the working flag is cleared. To do.

  In subsequent S340 to S360, similarly to S220 to S240 described above, various integral values used for the kickback determination are reset, and the process proceeds to S370. In step S370, the error flag is cleared. In step S380, the driving of the motor 20 is stopped, and the process proceeds to step S110.

  As described above, in the grinder 2 according to the present embodiment, the control circuit 80 as the control unit rebounds from the workpiece due to a change in the posture of the apparatus body of the grinder 2 rather than the rotation speed of the motor 20. Detecting that (ie kickback). Then, when the control circuit 80 detects kickback, the control circuit 80 stops driving the motor 20.

  For this reason, according to the grinder 2 of this embodiment, compared with the conventional apparatus which detects a kickback from the change rate of the rotation speed of the motor 20, the detection accuracy of a kickback can be improved. Therefore, it is possible to prevent the user from feeling uncomfortable by erroneously detecting kickback and stopping the driving of the motor 20.

  In this embodiment, the acceleration sensor 82 and the angular velocity sensor 84 are used to detect the movement speed and movement amount in the three axis directions, the angular velocity and the rotation angle around the three axes, and any one of these parameters is kickback. When the judgment value is exceeded, a kickback is detected.

For this reason, according to the grinder 2 of this embodiment, when a kickback occurs, the kickback can be detected more reliably from the posture change of the apparatus main body.
Further, the control circuit 80 detects the load applied from the tip tool 16 to the apparatus main body by the motor current when the motor 20 is driven, and the motor current exceeds the “threshold 1” for work start determination for a certain time “t1”. When elapses, a work flag is set and kickback determination is started.

  After that, when the motor current falls below the “threshold value 2” for work completion determination, and after a certain delay time “t2” has elapsed, the work flag is reset and the kickback determination is terminated.

  For this reason, in the present embodiment, the kickback determination period can be limited to a period in which kickback may occur due to driving of the motor 20, and kickback is performed under conditions where kickback does not occur. Can be prevented from being erroneously detected.

  In particular, in the present embodiment, the kickback determination is performed until a certain delay time “t2” elapses after the motor current falls below the “threshold value 2” for work completion determination.

  For this reason, even if the load applied to the motor 20 sharply decreases with the occurrence of the kickback and the motor current falls below the “threshold 2”, the kickback is detected from the change in the posture of the apparatus body detected thereafter. It becomes possible to detect, and the accuracy of kickback detection can be improved.

As mentioned above, although one embodiment of this indication was described, this indication is not limited to the above-mentioned embodiment, and can carry out various modifications.
For example, in the above embodiment, the acceleration sensor 82 and the angular velocity sensor 84 are used to detect the movement speed and movement amount in the three-axis directions, and the angular velocity and the rotation angle around the three axes, respectively, in order to detect kickback. did.

  However, the direction in which the device body rebounds from the workpiece and the rotation direction of the device body that occurs due to the rebound can be specified by the type of power tool and the work content, so kickback detection is performed according to the movement direction and rotation direction. Parameters may be set.

  That is, as a parameter for kickback detection, a parameter suitable for kickback detection of the electric tool is appropriately selected from the above-described movement speed and movement amount in the three axis directions and angular speed and rotation angle around the three axes. You may make it detect.

  In the above-described embodiment, the kickback determination period is set based on the motor current detected by the current detection circuit 58. However, the kickback determination period is determined by the tip tool during the machining operation of the workpiece. It suffices if the setting can be made based on the load applied from 16 to the apparatus main body.

  The load applied to the apparatus main body from the tip tool 16 can be detected not only from the motor current but also from the rotational torque of the motor 20, the rotational speed (rotational fluctuation) of the motor 20, and the like, and is generated in the apparatus main body. It can also be detected from vibration or the like. For this reason, the kickback determination period may be set by comparing these parameters with a threshold for determination during work.

  On the other hand, although the grinder 2 has been described as an example in the above-described embodiment, the power tool of the present disclosure is the above-described implementation as long as it is a power tool that rebounds from the work material due to a reaction force from the work material when the work material is processed. The same effect as the form can be obtained. Specifically, for example, an electric saw provided with a cutting blade or an electric chain saw may be used.

Moreover, although the grinder 2 of the said embodiment is an alternating current drive type, the electric tool of this indication may be a rechargeable electric tool which operate | moves by receiving electric power supply from the battery which can be charged.
In addition, a plurality of functions of one constituent element in the above embodiment may be realized by a plurality of constituent elements, or a single function of one constituent element may be realized by a plurality of constituent elements. Further, a plurality of functions possessed by a plurality of constituent elements may be realized by one constituent element, or one function realized by a plurality of constituent elements may be realized by one constituent element. Moreover, you may abbreviate | omit a part of structure of the said embodiment. In addition, at least a part of the configuration of the above embodiment may be added to or replaced with the configuration of the other embodiment. In addition, all the aspects included in the technical idea specified only by the wording described in the claim are embodiment of this invention.

  DESCRIPTION OF SYMBOLS 2 ... Grinder, 4 ... Motor housing, 6 ... Gear housing, 8 ... Rear cover, 9 ... Power cord, 10 ... AC power supply, 12 ... Spindle, 14 ... Inner flange, 16 ... Tip tool, 18 ... Lock nut, 19 ... Wheel Cover, 20 ... Motor, 30 ... Operation switch, 40 ... Capacitor, 42 ... Speed setting unit, 44 ... Display unit, 50 ... Controller, 52 ... Bidirectional thyristor, 54 ... Switch detection circuit, 56 ... Zero cross detection circuit, 57 ... Resistance 58, current detection circuit 60 drive circuit 70 power circuit 80 control circuit 82 acceleration sensor 84 angular velocity sensor

Claims (5)

A motor,
A drive circuit for driving the motor;
A control unit that controls driving of the motor via the driving circuit;
An apparatus main body in which the motor, the drive circuit, and the control unit are housed, and a tip tool that is rotationally driven by the motor can be mounted;
A detection unit for detecting a change in posture of the apparatus body;
With
The control unit determines that the apparatus main body has bounced off the workpiece when the attitude change amount of the apparatus main body detected by the detection unit exceeds a preset threshold when the motor is driven. A power tool configured to stop driving of the motor. The detection unit is configured to detect at least one of a movement speed and a movement amount of the apparatus main body in one or a plurality of axial directions as an attitude change amount of the apparatus main body.
The control unit is configured to stop driving the motor by determining that the apparatus main body has bounced off the workpiece when the moving speed or moving amount detected by the detecting unit exceeds a threshold value. The power tool according to claim 1, wherein The detection unit is configured to detect at least one of a rotation speed and a rotation amount around one or a plurality of axes of the apparatus main body as an attitude change amount of the apparatus main body.
The control unit is configured to stop the driving of the motor by determining that the apparatus main body has rebounded from the workpiece when the rotation speed or rotation amount detected by the detection unit exceeds a threshold value. The electric tool according to claim 1, wherein the electric tool is provided. The controller is
When the motor is driven, when the load applied to the apparatus main body from the tip tool is larger than a threshold value for determination during work, the electric tool includes a determination unit that determines that the workpiece is being processed. ,
When the determination unit determines that the power tool is processing the workpiece, whether or not the apparatus main body is rebounded from the workpiece based on the posture change amount of the apparatus main body. The power tool according to any one of claims 1 to 3, wherein the power tool is configured to be determined.   The determination unit is configured to allow the power tool to be in a state where the load falls below a threshold value for determining work completion after the load exceeds a threshold value for determining work start, and then a certain delay time elapses. The power tool according to claim 4, wherein the power tool is configured to determine that the workpiece is being processed.